feat(mediatek): add smcc call for MSDC

Some registers of MSDC need to be set in ATF, so we add MSDC drivers.

Change-Id: Idde51a136ad08dbaece0bdaa804b934fca7046b6
diff --git a/plat/mediatek/include/mtk_sip_def.h b/plat/mediatek/include/mtk_sip_def.h
index 7449371..907f0c1 100644
--- a/plat/mediatek/include/mtk_sip_def.h
+++ b/plat/mediatek/include/mtk_sip_def.h
@@ -11,6 +11,7 @@
 #define MTK_SIP_SMC_FROM_NS_EL1_TABLE(_func) \
 	_func(MTK_SIP_KERNEL_TIME_SYNC, 0x202) \
 	_func(MTK_SIP_KERNEL_DFD, 0x205) \
+	_func(MTK_SIP_KERNEL_MSDC, 0x273) \
 	_func(MTK_SIP_VCORE_CONTROL, 0x506) \
 	_func(MTK_SIP_IOMMU_CONTROL, 0x514) \
 	_func(MTK_SIP_APUSYS_CONTROL, 0x51E) \